This invention concerns a method for disposing of radioactive waste. More specifically, this invention concerns a method for ultimate disposal of high level liquid waste by dilution and confinement.
Spent fuel from nuclear reactors can be reprocessed to recover uranium (and plutonium, if desired). The reprocessing operation generates a residue of radioactive waste. The radioactive waste formed in reprocessing may be divided into three types: (1) high-level liquid waste (HLLW)--aqueous waste that contains almost all (more than 99%) of the fission and actinide products with a small amount of uranium and plutonium not recovered during reprocessing; (2) intermediate-level liquid waste (ILLW)--aqueous waste which contains much lower concentrations of fission products than HLLW and contains no appreciable amounts of uranium or plutonium; and (3) low-level liquid waste (LLLW)--waste which requires only minimal treatment before release to the environment. Reprocessing of nuclear plant fuel is discussed in Nuclear Technology, Volume 43, pages 244-258, (mid-April, 1979), the disclosure of which is incorporated herein by specific reference.
Ultimate disposal of HLLW presents a difficult problem to the nuclear power industry, in that some of the radioactive species present in HLLW are very long-lived. The discussions of nuclear waste disposal in the following references are incorporated herein by specific reference: Science, Volume 197, Pages 519-527 (Aug. 5, 1979); Oceanus, Volume 20, No. 1 (Winter, 1977); Nuclear Technology, Volume 44, Pages 284-296 (July, 1979); ERDA-76-43, Volume 1-5 (May, 1976). As exemplified in the discussions in the above-listed references, current proposals for disposal of HLLW have been directed primarily to concentration and confinement of HLLW. The principal example of concentration and confinement techniques is the proposed system in which radioactive waste is incorporated into a borosilicate glass or similar solid form with low-water leachability properties. The solid is then further containerized and placed in a location (such as a geological formation) where the HLLW is expected to be undisturbed and out of contact with the biosphere for a very extended period. However, this system results in a concentrated source of radioactive nuclides, and their decay heat release, with the resultant high temperatures, having a detrimental effect on the surrounding geological formation and longevity of the containment and leachability properties of the solid waste form. Failure of the containment and solid waste form will then lead to the release of radioactive nuclides at a very high local concentration, greatly increasing the concentration gradient through the geological formations back to the biosphere. The present invention involves a method for disposing of radioactive waste, such as HLLW, which overcomes the disadvantages of concentration and confinement techniques.